Which versions of pyrefly are malicious?

Every published version of pyrefly on npm is considered malicious. Remove the package entirely.

How do I remediate pyrefly if I installed it?

Remove pyrefly from your project and lockfile, then assume any secrets accessible to the build or runtime were exposed: rotate API keys, tokens, and credentials, and audit for unexpected outbound activity or persistence.

I already installed pyrefly — how do I know if it already compromised me?

If pyrefly was ever installed, its post-install/runtime payload may have already executed. O3's L7 egress monitoring and runtime eBPF sensors detect the credential exfiltration or command-and-control callback after install and block the malicious outbound channel, so you catch and contain the actual compromise — not just the presence of the package.

Is pyrefly part of a known attack campaign?

Yes — pyrefly is associated with the GHSA-2mj4-8c65-f5p4 campaign. Packages in the same campaign often share infrastructure and payloads, so check whether any related packages are also in your dependency tree.

How do I find pyrefly across my projects, lockfiles, and CI pipelines?

Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for pyrefly (all published versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging pyrefly across your stack and pipelines.

Malicious package

pyreflynpm

Malicious code in pyrefly (npm) Remove it immediately and rotate any exposed credentials.

MAL-2026-887

Immediate action

Remove the package, then rotate any secrets the build/runtime could reach.

npm uninstall pyrefly

What this malware does

The package pyrefly was found to contain malicious code.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.

Malicious versions

all versions

Every published version of this package is considered malicious — remove it entirely.

Indicators of compromise (SHA-256)

588445ae77d1fbd6e2123a29bd2331067492d3a518d7dbbc3a1d57a400622e83

f731c9ac1e4183a530b005b34a0e1331b1dc61ef8fc60aea56170766e444a48e

Detection & response playbook

Malicious package

Find it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for pyrefly (all published versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging pyrefly across your stack and pipelines.
If you installed it — respond
Remove pyrefly from your project and lockfile, then assume any secrets accessible to the build or runtime were exposed: rotate API keys, tokens, and credentials, and audit for unexpected outbound activity or persistence.
Did it already run?
If pyrefly was ever installed, its post-install/runtime payload may have already executed. O3's L7 egress monitoring and runtime eBPF sensors detect the credential exfiltration or command-and-control callback after install and block the malicious outbound channel, so you catch and contain the actual compromise — not just the presence of the package.
How O3 protects you
O3 blocks pyrefly before install through its supply-chain scanner, and if it has already run, detects and severs the exfiltration or C2 callback at runtime through L7 egress monitoring and eBPF.

Frequently asked questions

No. pyrefly on npm has been identified as a malicious package (all published versions flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

GHSA-2mj4-8c65-f5p4

References

github.com

Credits

Amazon Inspector · finder

Detect & block this

O3 blocks pyrefly-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the malicious outbound activity and severs the channel.

Malware detection Runtime egress monitoring